Method for treating ferrous metals



United States Patent METHOD FOR TREATING FERRQUS METAIS Wallace T. McMichael, Lake Jackson, Tex., and John C. Robertson, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed Feb. 23, 1965, Ser. No. 434,634

6 Claims. (Cl. 75130) ABSTRACT OF THE DISCLOSURE A treating agent and process for treating molten ferrous based materials, particularly cast iron, comprising from about to about 45 percent aluminum carbide and from about 95 to about 55 percent magnesium oxide, or alternately this quantity of aluminum carbide with from about 85 to 20 percent magnesium oxide and from about 80 to about 10 percent of calcium oxide, calcium carbide and mixtures thereof. This invention provides for retention of a desirably high magnesium concentration in the melt and simultaneously, with cast iron, gives substantially complete nodularization of graphite present in the melt.

This invention relates to the treatment of molten ferrous based materials, and more particularly is concerned with a novel process for preparing ductile, i.e. nodular, grey cast iron.

It is known in the art that magnesium over and above that required for desulfurization retained in cast iron will cause uncombined carbon present therein to be present in a compacted form, and preferably a spheroidal form. Such cast iron is known as nodular iron and possesses properties different from and improved over that found in grey cast iron Where the uncombined carbon is present as the normal flake graphite. The terms nodular iron or nodularization as used hereinafter refer to iron having spheroidal, i.e. compacted graphite inclusions and to the process by which these are formed.

A wide variety of processes and apparatus have been set forth in the art relating to the introduction of magnesium into molten cast iron. Many of these known techniques employ complicated equipment or use compositions whereby undesirable substances are introduced into the molten ferrous bath along with the magnesium. Also, violent, uncontrolled hazardous reactions accompany addition of magnesium into the iron in the employment of a majority of such known processes. Now, unexpectedly a safe, simple, easy to handle composition and process has been found to introduce magnesium into a ferrous based melt.

It is a principal object of the present invention, therefore, to provide a novel process for introducing magnesium into molten ferrous based melts and for producing nodular iron whereby a rapid, but non-violent reaction is achieved with substantially complete nodularization of the graphite in the iron product along with the establishment of a desirably high residual magnesium content in the treated iron.

It is another object of the present invention to provide an inexpensive composition and process for nodularizing two.

It is a further object of the present invention to provide a process suitable for use in nodularizing iron which obviates the need for special plunging equipment to introduce a treating agent under the bath surface and requires no complicated mechanical application equipment.

It is still another object of the present invention to provide a nodularizing composition and process which is safe to use and operate and which obviates the need for 3,367,772 Patented Feb. 6, 1968 covered ladles or other special pressure resistant equipment as are employed in many conventional nodularizing processes.

It is an additional object of the present invention to provide a process for treating molten ferrous materials that does not introduce undesirable constituents, which may alloy with the melt, into the ferrous melt.

It is a further object of the present invention to provide a process for nodularizing iron wherein alloying elements are not introduced into the melt as in many conventional magnesium treatments. This instant invention thereby permits (1) the incorporation of large quantities, 70 percent or more, of gates, risers and other scrap into subsequent melts without adversely affecting the properties oi the iron, and (2) the use of heavier post inoculation treatment which is particularly desirable for thin sectioned castings.

It is another object of the present invention to provide a means for nodularizing iron wherein there is substantially no loss of the ferrous-based melt because of spillage, splattering or other violent melt reaction during the treatment.

These and other objects and advantages will become apparent from the detailed description presented hereinafter.

In accordance with the present invention, substantially complete nodularization of graphite and retention of a desirably high magnesium concentration in cast iron is produced without violence by introducing an addition agent comprised of from about 5 to about 45 and ordinarily from about 20 to about 40 weight percent aluminum carbide and from about 95 to about 55 and ordinarily from about to about 60 weight percent magne sium oxide into a molten iron bath. Preferably about 37 weight percent aluminum carbide and about 63 weight percent magnesium oxide is used.

Although the process proceeds satisfactorily with this composition substantially complete .nodularization is achieved at substantially the same reaction times but at even a smoother reaction activity if a member selected from the group consisting of calcium oxide, calcium carbide and mixtures thereof is incorporated into the treating agent composition. Therefore, ordinarily a composi-' tion comprising, on a weight basis from about to about 20 percent magnesium oxide, from about 80 to about 10 percent of a member selected from the group consisting of calcium oxide, calcium carbide and. mixtures thereof and from about 5 to about 45 percent particulate aluminum carbide is introduced as the addition agent into a molten grey iron bath maintained at a temperature of from about 2450 to about 3000 F., and preferably at from about 2600 F. to about 3000" F.

Preferably with the magnesium oxide-calcium oxidealuminum carbide reaction mixture, this treating agent composition comprises about 33.5 weight percent magnesium oxide, about 46.5 weight percent calcium oxide and about 20 weight percent aluminum carbide.

With the magnesium oxide-calcium carbide-aluminum carbide reaction mixture the treating agent composition preferably employed in the present novel process comprises about 48 weight percent magnesium oxide, about 38 weight percent calcium carbide and about 14 weight percent aluminum carbide.

The amount of the nodularizing agent to be employed in treating a molten mass of a ferrous based material, e.g. grey iron, by the instant process, expressed as pounds of magnesium metal equivalent per ton of cast iron, ranges from about 0.5 to about 25 pounds magnesium per ton of the ferrous based material. Ordinarily, the composition is added in a concentration of from about 1 to about 10 pounds of magnesium (metal equivalent) per ton of cast iron.

The treatment time employed ranges from about 0.25 to about 20 minutes, ordinarily from about 0.5 to about 8 minutes and preferably the-reaction is carried out over a period of from about 1 to about minutes.

The magnesium oxide and calcium containing materials as used in the present composition are finely divided and ordinarily are in powder form. Also, preferably these are substantially anhydrous.

High grade, separate components, e.g. MgO, CaC and CaO can be used. Alternatively, burnt dolomite which contains both C210 and MgO as well as trace amounts of other oxides can be employed. With this latter material additional MgO, as needed, can be added to provide the hereinbefore specified operable quantities of MgO and CaO in the final composition. Other metal oxide generating substances such as magnesium silicate, magnesium hydroxide, calcium hydroxide and naturally occurring oxidic materials such as olivine [(Mg, Fe) SiO and the like can be employed.

The aluminum carbide employed in the present invention also is in particulate form and usually finely divided form; i.e. a powder.

An added advantage of the use of present composition in the present novel process is the residue remaining after reaction of the present treating agent in a molten ferrous melt can be heated to a minimum temperature of about 2200 K. in the presence of added carbon to regenerate additional aluminum carbide for reuse. This indicates that the basic raw. materials are MgO, or dolomite, and carbon.

The reactants can be blended by simple mixing operations and introduced as a particulate mix into the molten ferrous based bath to be treated by any of a variety of conventional means, e.g. plunging bells, etc., as known to one skilled in the art.

The composition is readily introduced into the bath if first fabricated into briquettes, compacts, pellets, bricks or other such similar shapes. By preparing such compacted masses, the amount of active ingredients added to a given mass of molten metal can easily and accurately be controlled. Simple pressure compacting of the ingredients without using binder constituents is preferred in the preparation of the compacts. For certain operations these compacts also may be sintered.

The compacted mass, e.g. in briquette form, conveniently is introduced under the surface of a melt by use of a standard perforated plunging device as employed in many ordinary nodularization techniques. Alternatively, the briquette can define an opening passing therethrough and a predetermined number of briquettes can be placed on a stick or rod and this assembly then be plunged into the mass to be treated.

A particularly effective and simple way to introduce the reactants into the molten iron is to afiix the requisite quantity of the briquettes or blocks to the bottom of the ladle. By this technique, the nodularization promoting agent is already in place prior to the time the molten iron is introduced into the pot. Also, this technique assures that the compacts are positioned at a predetermined spot usually near or in the bottom of the ladle or metal treatment pot.

The size of the compacts, i.e. briquettes, for example, to be employed in the instant process is not critical. For optimum efficiency of operation, however, ordinarily the compacts are provided so as to have a minimum surface area to volume ratio of about 5. Ordinarily, to increase the effective surface area, a plurality of members rather than a single large brick or block is employed for a given treatment. However, even with ladies holding as much as 400 pounds or more iron, one briquette designed to have the requisite surface area/volume ratio, as by multiple perforations or wafile effect, for example, satisfactorily can produce the desired nodularization The resulting nodular iron product can be used in any application and/or subsequently processed by any of the techniques employed for ductile iron.

Although the present invention finds particular utility in the nodularization of iron, it also finds application in Wt. percent C 3.2-3.5

S OHM-0.008

Fe, balance.

Power of about 6 kilowatts was applied to the furnace containing about 3.5 pounds of the iron for a period of about one hour. The temperature of the molten mass was read with an optical pyrometer and was held essentially constant at a temperature of about 2800 F. over the test period.

A 38 gram cylindrical briquette about 1.5 inches in diameter of the present treating agent composed of about weight percent of a dead burned powdered dolomite (58 weight percent CaO, 40 weight percent MgO, balance substantially other metal oxides), and 20 weight percent aluminum carbide powder (about 80 percent passing through a 325 U.S. Standard mesh sieve) was prepared as follows. This is equivalent to about 9 pounds magnesium per ton of iron.

The powdered mix components in the requisite amounts were blended together and compressed into the cylindrical briquette by compacting in a mold at a pressure of about 4000 pounds per square inch. The resulting briquette was perforated with four At-inch diameter holes. The briquette was placed on the end of a graphite rod and plunged into the molten metal and maintained therein for a total period of about 2 minutes. Reaction, indicative of magnesium liberation, started after the briquette had been in the melt for about seven seconds. Reaction activity peaked at about 30 seconds and continued vigorously for a total of about one minute after the immersion and then began to subside. The reaction was still proceeding actively at the end of the two minute immersion period at which time the remaining portion of the briquette was withdrawn from the melt. At no time during the reaction period was there violent reaction or any splattering of ferrous metal from the furnace. After removal of the briquette from the melt, about 15 grams of percent ferrosilicon was stirred into the melt as a post-inoculant in accordance with standard procedure. The power to the furnace was then shut off and the treated metal poured into a Y-bloc'k shell mold for the purpose of obtaining four one-fourth inch diameter sample specimens according to the standard ASTM procedure A-445-60T.

Metallographic examination of the iron produced showed a fully nodular graphite microstructure.

The casting was sampled by drilling and analyzed by emission spectroscopy. This analysis showed 0.02 percent residual magnesium retained in the cast product.

Example lI.Using the same experimental apparatus and procedure as described for Example I, a 23.4 gram briquette was made. This was comprised on a weight basis of about 38.1 percent finely divided calcium carbide (CaC about 47.6 percent powdered MgO and about 14.3 percent aluminum carbide (Al C This briquette was used to treat a 36 pound cast iron remelt charge maintained in the 6-kilowatt induction furnace at about 2850 F.

The briquette had a magnesium equivalent of about 8 pounds magnesium metal per ton of iron. A total treat-.

ment time, i.e. immersion of the briquette in the melt, of about 3 minutes was employed. In this test the compact was broken into pieces and these loaded into a slotted graphite plunging belt which was used to immerse the treating agent in the melt. About 20 seconds elapsed before observable reaction started. Once under way, the reaction continued actively, but somewhat less vigorously than with the composition used in Example I and was still progressing well when the briquette was removed from the melt after the 3 minute immersion period. After the plunger was removed from the melt, the cast iron was post-inoculated with about 15 grams of 85 percent ferrosiiicon in accordance with standard practice and the melt cast in a shell mold.

The resulting solidified iron product was found upon metallographic examination to contain graphite only in spheroidal form.

Example III.-The same compacting techniques used with a blended powdered mixture of about 37 weight percent aluminum carbide and about 63 weight percent magnesium oxide produced cylindrical compacts. These when introduced into molten ferrous melts for periods of from about 1 to about 5 minutes in amounts to provide from about 1 to about 10 pounds of magnesium per ton of melt in accordance with the techniques described in Example I gave active, but non-violent reactivity, and provided substantially complete nodularization of the graphite in the iron plus retained magnesium alloyed in the resulting iron product.

In a manner similar to that described for the foregoing examples, the following compositions can be employed in the process of the present invention:

Weight percent 1) Al C powder 20 MgO (-200 mesh U.S. Std Sieve) 33.5 CaO ('200 mesh U.S. Std Sieve) 46.5

(2) Al C particle 20 MgO powder 60 0210 (325 mesh U.S. Std Sieve) 20 (3) A1 powder 25 MgO powder 55 CaO powder 20 (4) Al C powder 1O MgO -325 mesh U.S. Std Sieve) 70 CaO (:100 mesh U.S. Std Sieve) 20 (5) Al C chunk (100 to 200 mesh U.S. Std

Sieve) 20 CaO powder CaC powder MgO powder 50 (6) Al C (-30 to 100 mesh U.S. Std Sieve) 5 MgO powder 95 These compositions can be simply admixed and injected as a particulate mass into a molten cast iron, molten steel bath, a molten blast furnace iron or can be compacted prior to use in such ferrous based melts.

Various modifications can be made in the present invention without departing from the spirit and scope thereof for it is understood that we limit ourselves only as defined in the appended claims.

We claim:

1. A process for treating ferrous based melts which comprises;

(1) introducing into a molten mass of a ferrous based metal an addition agent comprising from about 5 to about 45 weight percent aluminum carbide and from about 95 to about 55 weight percent magnesium oxide, and

(2) maintaining said agent in said mass for a period of time ranging from about 0.25 to about 20 minutes,

(3) removing from the molten ferrous based metal the residue remaining after reaction of said addition agent in said molten ferrous melt, and

(4) heating said residue to a minimum temperature of about 2200" K. in the presence of added carbon thereby to regenerate additional aluminum carbide for use in preparation of additional quantities of said addition agent.

2. The process as defined in claim 1 wherein the molten mass of ferrous based metal is a grey cast iron and said iron is treated with an addition agent comprising from about 20 to about 40 weight percent aluminum carbide and from about to about 60 weight percent magnesium oxide, the amount of said agent, expressed as pounds of magnesium metal equivalent per ton of iron being from about 0.5 to about 25, and the agent is maintained in said molten mass for a period ranging from about 0.5 to about 8 minutes.

3. The process as defined in claim 2 wherein from about 1 to about 10 pounds of said agent, expressed in pounds of magnesitun metal equivalent per ton of metal, is introduced into the molten mass of grey cast iron and maintained in the molten mass for a period of from about 1 to about 5 minutes.

4. A process for treating ferrous based melts which comprises:

(1) introducing into a molten mass of a ferrous based metal an addition agent comprising from about 5 to about 45 weight percent aluminum carbide, from about to about 20 weight percent magnesium oxide and from about 80 to about 10 weight percent of a member selected from the group consisting of calcium oxide, calcium carbide and mixtures thereof, and

(2) maintaining said agent in said molten mass for a period of time ranging from about 0.25 to about 20 minutes,

(3) removing from the molten ferrous based metal the residue remaining after reaction of said addition agent in said molten ferrous melt, and

(4) heating said residue to a minimum temperature of about 2200 K. in the presence of added carbon thereby to regenerate additional aluminum carbide for use in preparation of additional quantities of said addition agent.

5. The process as defined in claim 4 wherein the amount of said agent, expressed as pounds of magnesium metal equivalent per ton of iron is from about 0.5 to about 25, and the agent is maintained in said molten mass for a period ranging from about 0.5 to about 8 minutes.

6. The process as defined in claim 5 wherein from about 1 to about 10 pounds of said agent, expressed as pounds of magnesium metal equivalent per ton of metal, is introduced into the molten mass of grey cast iron and maintained in the molten mass for a period of from about 1 to about 5 minutes.

References Cited UNITED STATES PATENTS 2,552,204 5/1951 Morrogh 75-129 X 2,785,970 3/1957 Loria 75-129 X 2,963,364 12/1960 Crockett et al. 75-130 3,197,306 7/1965 Osborn et al. 75-130 3,290,142 12/1966 Loomis 75-l30 X DAVID L. RECK, Primary Examiner. H. TARRING, Assistant Examiner. 

